Nanotechnological Approach to Improve Water and Wastewater Treatment Processes: Concept, Recent Advances, and Challenges

1. Introduction

Water is one of the vital natural resources and a necessity without which no life will survive on this planet. Even though water makes up over 70% of the Earth's surface, only 2.5% of it is really consumable. The different sources of freshwater are groundwater, river, glacier, and atmospheric water vapor. The sustainability of human life is dependent on the availability of water in its pure form. The pollutants are added to the environment through human activities or industrial processes (Chaturvedi et al., 2019; Patanjali et al., 2019). The most crucial step is making sure everyone has access to safe, affordable water at the same time globally a grand challenge. Millions of people suffer from diseases mediated through contaminated water. According to a report by the World Health Organization (WHO), about 12 million individuals die every year from diseases associated with water. Around 90% of all diseases are caused by impure water in developing countries. Almost all the sources of natural freshwater are contaminated. Even the water rich countries are also inescapable from water scarcity due to the growing modern civilized industries, human population, and agricultural activities. Fresh, potable water is a global resource that is becoming difficult to obtain. Millions of lives have been lost every year due to unsafe water, and an estimated 1.2 billion people worldwide lack access to safe drinking water. (Montgomery & Elimelech, 2007; Shannon et al., 2008). The natural quality of the water has been compromised by the introduction of toxic pollutants from a variety of sources. The extensive use of chemically prepared pesticides in the farming fields is deteriorating groundwater quality. Due to different human activities, harmful contaminants are entering water supply systems worsening public health. It is anticipated that existing water problems will become much more severe over the next several years. Worldwide water shortage is occurring as a result of droughts, rising population, and increased urbanization. There are predictions that the global population will reach roughly nine billion by the year 2050, and that by the year 2075, nearly 75% will be affected by clean water shortages (Kargari & Shirazi, 2014; Tlili & Alkanhal, 2019). It is, therefore, of the highest significance to do an extensive study on the issue of providing people with access to clean and safe water. Intestinal parasitic infections and diarrheal have become major concerns regarding malnutrition as a result of poor digestion of food by people who have been sickened by water (Lima et al., 2000; Shannon et al., 2008). Bacteria and enteric viruses found in water are to blame for these illnesses. Human activities are responsible for the introduction of a significant number of pollutants into the municipal water supply systems of both developing countries and developed nations, which raises worries about both public health and the environment. In order to solve these widespread issues, significant research needs to be conducted into innovative methods of water treatment that offer financial advantages and require only a small amount of energy, while also minimising the consumption of chemicals and their impact on the surrounding environment. Existing water and wastewater treatment methods include liquid distillation, anion exchange, ultrafiltration, adsorption via activated carbon, reverse osmosis, deionization, and ultraviolet (UV) filtration. Such conventional processes involve high investment costs and low output-input ratio, and sometimes can be inefficient too. Nearly about 2-3% of the nation’s total energy is consumed by water treatment processes. Biological treatment plants consume a major part of the total energy used in water treatment. To this end, there is a pressing want for more efficient, low-cost, technologically superior, and robust methods of water treatment with the involvement of minimal energy, and chemicals, and having low direct or indirect impact on the environment and human life (Chaturvedi et al., 2019; Patanjali et al., 2019; Qu et al., n.d.; Tlili & Alkanhal, 2019).